Carbon dioxide ice on Mars, computer artwork. This area is part of the carbon dioxide ice cap at the Martian South Pole. The large pits are where the carbon dioxide ice cap has sublimed to reveal ice layers below the surface. Mars is much colder than Earth, and has a thin atmosphere of carbon dioxide. Temperatures at the Martian south pole are low enough to maintain a residual carbon dioxide ice cap during the summer. Observations by the Mars Global Surveyor have shown that this carbon dioxide ice cap is gradually shrinking as these pits are enlarged each summer. This has been interpreted as evidence that the Martian climate is slowly warming. The surface dust is redbrown due to the high iron content of the rocks.